THERMAL-METALLURGY  OF 


ZING  ALLOYS 

BY 

AMBROSE  ALLEN  ARNOLD 


THESIS 

FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CHEMICAL  ENGINEERING 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 
UNIVERSITY  OF  ILLINOIS 


1921 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/thermalmetallurgOOarno 


/ 92/ 
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UNIVERSITY  OF  ILLINOIS 

i92_^__ 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 
AMBR 0 SE_  ALLBML  A M OLD. 

ENTITLED I lijiIEiiu.  TALL.U  RG- Y-  -Q£  - - ALL-Q  Y-S 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF J3ac h P..1  or  — Qf— Sc-i^nc e _ All A iaert.  ia  £t  X_ tie. ing 


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Instructor  in  Charge 


Approved  : (A 


HEAD  OF  DEPARTMENT  OF 0- HEm  TS  ARY 


*J'<s 


S0189 


C-Q-JS-T-E-N-T-S 


Introduction 

Pages 

Zinc  - Tin  Alloys 

Page 

Graphs 

11 umbers 

1-12. 

Zinc  - Lead  - Tin  Alloys 

Pages 

Graphs 

numbers 

13-24. 

- 

- 


THERMAL  METALLURGY  OP  ZIUC  ALLOYS 

Zinc  is  practically  in  its  infancy  as  far  as  its  possible 
exploitation  of  uses  is  concerned.  In  order  to  discover  new  appli- 
cations it  is  necessary  to  understand  zinc  and  its  varying  condi- 
tions. That  has  been  the  objeot  of  this  investigation  — How  does 
Zinc  behave  when  alloyed  with  certain  other  metals? 

In  order  the  better  to  understand  metals,  a comparatively 
new  branch  of  scientific  endeavor  has  recently  been  given  more 
attention  — that  of  Physical  Metallurgy.  The  scope  of  Physical 
Metallurgy  is  exceedingly  wide  and  makes  generous  use  of  chemistry, 
physics,  mechanics  (strength  of  materials) .crystallography,  and 
Thermal  analysis. 

It  is  in  part  to  the  latter  division  — thermal  analysis  — 
that  this  study  directs  itself  in  so  far  as  certain  Zinc  alloys  are 
concerned  — Zn— Sn,  and  Zn  - Pb  - Sn  - although  thermal  relations 
of  metallic  alloys  have  been  given  some  attention,  it  is  a compara- 
tively new  consideration  and  much  work  remains  to  be  done.  A survey 
of  the  literature  gave  no  evidence  of  any  work  along  the  lines  of 
this  particular  investigation,  alloys  of  zinc  and  tin,  and  of  zinc 
lead,  and  tin.  Excellent  work  had  "been  carried  on  with  some  of  the 
more  common  alloys  used  in  everyday  metallurgical  practice,  notably 
that  of  iron,  carbon,  and  copper,  and  also  a few  zinc  combinations. 

A study  of  the  changes  which  occur  when  metals  are  heated  and  cooled 
has  thrown  much  light  on  the  constitution  of  those  metals  and  their 
alloys.  The  following  have  done  work  along  these  lines :- 

Metallic  Alloys  William  T.  Brannt. 

Introduction  to  Physical  Metallurgy 

Walter  Bosenhain 


Metallurgy  of  the  Common  Metals 


. 


• 

— 

'• 


' . 


. • j 

» 

* 


. 


-2- 


The  Physical  Chemistry  of  the  Metals 

Rudolph  Schenck. 

Translated  by  Reginald  Scott  Dean. 

Traite  de  Metallographic  Felix  Robin 

The  Elements  of  Metallography  Rudolph  Ruer. 

Translated  by  C.  H.  Mathews on. 

Chemische  Technologic  Der  Legierungen 

Dr.  P.  Runglass 

A Treatise  on  Brasses,  Bronzes,  and  other  Alloys 

Robert  H.  Thurston. 

Metallogrphy  Cecil  H.  Desoh. 

Alloys  and  their  Industrial  Applications, 

Edward  F,  Law. 

There  are  various  methods  of  making  cooling  curves,  de- 
pending upon  methods  of  heating  and  methods  of  plotting.  For  heat- 
ing purposes,  furnaces  of  the  gas  or  electical  resistance  types  are 
commonly  employed.  In  this  investigation  a gas  furnace  was  used. 
There  are  three  distinct  methods  of  plotting  data:  first,  "time  - 
temperature,”  which  is  simplest  and  gives  behavoir  of  metal  in  most 
direct  way;  second,  "inverse  rate,”  for  which  the  observer  notes 
the  time  intervals  occupied  by  the  metallic  solution  in  rising  or 
falling  through  successive  equal  differences  of  temperature  and  plots 
a curve  whose  ordinates  are  T (temperature)  and  whose  abscissae 
are  ^ where  t is  time  and  T is  temperature;  third,  the  "differ- 
ential" and  "derived  differential"  in  which  the  rate  of  heating  or 
cooling  of  the  metal  under  investigation  is  compared  with  a stand- 
ard piece  of  metal  placed  in  the  same  furnace  and  treated  under  the 
same  conditions  at  the  same  time.  In  this  investigation  the  first, 
or  "time-temperature"  method  of  plotting  cooling  curves  was  followed. 
It  is  easily  the  simplest  and  for  this  purpose  seemed  sufficiently 
adequate. 


. 


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[.  ■ ■ ' ' ",  . ; , 




. 

r.; 

. 


-3- 


The  procedure  was  simply  to  get  a melt  of  the  alloy,  in- 
sert a thermo  oouple  and  read  temperature  as  it  cooled,  at  one 
minute  intervals,  and  plot  the  data  on  graph  paper.  Wherever  a 
flattening  of  the  curve  is  evident,  at  that  temperature  a solidi- 
fication took  place. 

An  ordinary  pot  furnace  was  used  into  which  air  and  gas 
in  proper  proportions .admitted  under  the  usual  laboratory  pressures, 
were  burned.  This  furnaoe  was  thoroughly  saturated  with  heat  to  a 
temperature  several  hundred  degrees  higher  than  that  required  for 
the  melt  in  order  that  the  radiation  of  heat  might  be  slower  and 
more  uniform.  This  is  an  important  precaution  as  was  learned  by 
experience.  A mixture  of  the  metallic  constituents  in  granulated 
form,  chemically  pure,  200  grams  in  weight,  was  placed  in  a fire 
clay  crucible  and  covered  with  about  one  quarter  inch  of  pulver- 
ized bone  charcoal.  The  crucible  and  its  contents  were  then  placed 
in  the  furnace  until  a good  melt  was  assured.  The  heavy  covering 
of  bone  charcoal  prevented  oxidation.  The  melted  solution  was  then 
thoroughly  stirred  with  a steel  spatula,  a thermo  couple  inserted 
into  the  melt,  the  gas  and  air  turned  off,  all  openings  carefully 
covered  with  heavy  asbestos  sheets,  and  the  regular  readings  were 
then  taken.  The  graphs  show  that  all  readings  were  begun  at  525  C. 
As  a matter  of  fact  the  cooling  usually  started  at  600  C,  By  the 
time  the  thermo  couple  indicated  525  C the  rate  of  heat  radiation 
was  quite  uniform.  While  the  diagrams  indicate  only  fifty  minutes 
for  each  "run",  some  of  the  melts  were  continued  for  longer  periods 
with  the  same  evidence  — namely, that  the  cooling  continued  to  drop 
regularly. 


A portable  Hoskins,  type  (PA),  pyrometer,  frequently 


. 


. 


-4 


calibrated,  was  constantly  used  throughout. 

The  melting  points  of  the  metals  concerned  are  as  follows:- 


Zinc 

419 

C 

Lead 

327 

C 

Tin 

232 

C 

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. 


p 


c- 


■( 


' ; , 


■ 

. 


. 


J- 


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5r\ 


5- 


A study  of  the  graphs  for  the  binary  system,  Zn  - Sn, 
readily  shows  that  as  the  percentage  of  Zinc  decreased  and  that  of 
Tin  increased  the  melting  points  decreased  in  value.  This  is  to  be 
expected  when  a substance  of  a low  melting  point,  Sn  at  327  C,  is 
added  to  one  of  a higher  melting  point,  Zn  at  419  C and,  since  a 
flattening  of  the  curve  took  place  but  once  in  each  instance,  it 
follows  that  Zn  and  Sn  are  soluble  in  each  other  in  all  proportions 
considered. 


The 

points  of  the 


following  summary  will  briefly  indicate  the  melting 
different  alloys 


Zinc 

Tin 

MP 

* 

$ 

C 

100 

— 

419 

95 

5 

410 

90 

10 

400 

85 

15 

397 

80 

20 

395 

75 

25 

393 

70 

30 

390 

65 

35 

385 

60 

40 

380 

55 

45 

373 

50 

50 

365 

These  results  have  also  been  plotted  — temperature 
against  percentage  composition,  on  the  Zn  - Sn  equilibrium  curve, 
which  will  give  a visualized  representation  of  the  same  data  (See 
graph  Ho,  12.) 


■ 


- 


o 

o 

Y? 

$ 

<V 

O 

**> 

<N 

^ ^ i- 


3-  ^ 

rr± 


-6 


The  binary  system  is  comparatively  simple*  When  the 
ternary  system  however  is  considered, a number  of  irregularities  are 
at  once  evident.  Zn  - Pb  - Sn  are  not,  soluble  in  each  other  in 
all  proportions.  This  is  borne  out  by  the  fact  that  in  some  in- 
stances the  curve  has  flattened  out  in  as  many  as  three  distinct 
places. 

A composition  of  90$  Zn  - 5$  Pb  - 5$  Sn  was  uniformily 
soluble.  The  next  graph  (number  14)  shows  a remarkable  change. 

Some  of  this  solution  seems  to  have  solidified  at  419  C,  the  melt- 
ing point  of  Zinc,  a second  solidification  at  405  C,  and  a third 
at  325  C,  close  to  the  melting  point  of  Lead.  From  these  facts, 
as  verified  in  other  alloys,  are  shown  that  some  of  the  Zinc  went 
out  of  solution  in  its  pure  state  and  solidified  at  419  C;  that 
a solution  of  some  mixture,  presumably  Zn,  Pb,  and  Sn,  solidified 
at  4o5  C;  and  finally  that  some  of  the  uncombined  Lead  went  out  of 
solution  very  close  to  its  usual  melting  point,  327  C.  From  such 
data  we  must  gather  that  a mixture  of  that  composition  upon  complete 
solidification  is  anything  but  uniform  in  texture.  Strangely  enough 
graph  15  shows  that  the  constituents  are  completely  soluble  in  one 
another.  The  very  next  composition,  graph  16,  shows  another  radical 
change.  In  the  latter  instance  another  three  fold  solidification 
took  place  - no  separation  of  a pure  element  this  time,  but  rather 
three  distinct  combinations  solidifying  at  397  C,  380  C,  and  295  C 
respectively.  A natural  inference  would  be  that  all  the  Zinc  had 
fallen  out  in  the  first  two  separations  and  that  in  the  latter  case 
lead  and  tin  alone  had  combined. 

A comparison  of  #16  and  #17  shows  that  although  the  lead 
control  of  the  latter  was  more  than  that  of  the  former,  yet  the 


-Y- 


initial  melting  point  of  the  former  was  higher  than  that  of  the 
latter;  while  the  final  solidification  of  the  latter  is  higher  than 
that  of  the  former.  The  most  logical  explanation  of  this  phenomena 
seems  to  he  that  in  #17  a larger  part  of  the  lead,  in  an  uncomhined 
state,  fell  out  at  325  C - near  its  ordinary  melting  point. 

lumber  18  in  which  70 $ Zn  was  also  employed,  shows  that 
no  lead  fell  out.  This  is  not  unusual  since  the  lead  content  of 
the  alloy  was  only  10$,  There  was  a double  solidification,  at  390  C 
and  at  380  C.  This  held  true  over  a very  small  range  of  temperature 
only  10  . In  #17  there  was  a marked  tendency  toward  a close  double 

solidification,  which  probably  took  place  in  a small  degree,  the 
heat  radiation  of  the  furnace  being  too  rapid  for  the  thermocouple 
to  make  the  proper  registration, 

60$  Zinc  was  contained  in  the  alloys  indicated  on  graphs 
# 19,  #20,  and  #21.  It  is  of  interest  to  note  the  similarity  of 
graphs  #16  and  #19,  the  former  containing  70$  Zinc  and  the  latter 
60$  Zinc.  In  both  cases  the  first  two  solidifications  took  place  at 
the  same  temperatures  395  C and  380  C and  practically  during  the 
same  time  intervals.  Why  this  should  be  true  is  difficult  to  de- 
termine, The  latter  alloy  had  10$  lead  and  that  may  be  one  of  the 
contributing  factors.  Of  the  three  alloys  containing  60$  Zinc  only 
one  of  them,  #20,  shows  any  evidence  of  a third  solidification,  at 
320  C which  was  very  likely  caused  by  a freezing  out  of  some  lead 
and  tin. 

Alloys  #22,  #23,  and  #24  contained  50$  Zinc.  #22,  with 

35$  lead,  shows  a deposition  of  that  metal  alloyed  with  tin  at  300  C. 
The  initial  freezing  point  was  at  400  C which  is  higher  than  for 
the  other  two  alloys.  #23  and  #24,  on  the  other  hand,  show  a 


. 

_ 

. 

• 

. 

. 

■ 


. 


. 


. 


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. 


-8- 

triplicate  solidification  in  each  instance.  This  is  undoubtedly  due 
to  the  increase  of  the  tin  content  with  which  the  Zinc  and  some  lead 
readily  alloyed  themselves.  In  #23  some  lead  fell  out  in  an  isolat- 
ed way.  That  this  did  not  hold  true  for  #24  is  evident  from  the  fact 
that  the  freezing  temperature  there  was  340  C which  is  13  higher 
than  the  melting  point  of  pure  lead.  This  shows  that  some  zinc  must 
have  had  an  influence  in  the  rise  of  temperature. 

The  following  summary  will  briefly  indicate  the  melting 
points  of  the  different  alloys:- 


1o 

* 

i 

Soli 

d 

i f 

ications. 

Zn 

Fb 

Sn 

1 

2 

3 

90 

5 

5 

415 

— 

— 

80 

10 

10 

420 

405 

325 

70 

25 

5 

400 

— 

— 

70 

20 

10 

397 

380 

295 

70 

15 

15 

405 

395 

325 

70 

10 

20 

390 

380 

— 

60 

30 

10 

397 

380 

... 

60 

20 

20 

400 

380 

320 

60 

10 

30 

380 

360 

50 

35 

15 

400 

— 

297 

50 

25 

25 

395 

370 

325 

50 

15 

35 

380 

360 

340 

That  Zn  - Pb 

- Sn  will  not  combine 

in 

all 

proportions  is 

amply  borne  out  by  the 

evidence  of 

the  above 

experiments.  This, 

likewise , 

indicates  that  there  must 

be  a wide 

range 

in  the  texture 

. 

• 

-9- 


of  the  alloys  — some  will  have  higher  tensile  strengths,  some  will 
withstand  more  compression,  than  others.  Their  molecular  struct- 
ures must  greatly  vary  as  a microscopic  study  would  undoubtedly 
reveal.  This  much  given  as  a clue  as  to  what  might  he  expected, 
further  investigations  are  necessary  to  determine  certain  other 
qualities  more  definitely. 


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